United States Patent 19 · 5,449,724 1. STABLE FREE RADICAL POLYMERIZATION PROCESS AND THERMOPLASTIC MATER ALS PRODUCED THEREFROM BACKGROUND OF THE INVENTION This invention relates

United States Patent 19 Moffat et al.

54). STABLE FREE RADICAL POLYMERIZATION PROCESS AND THERMOPLASTIC MATERALS PRODUCED THEREFROM

75 Inventors: Karen A. Moffat, Brantford; Marko D. Saban, Etobicoke; Richard P. N. Veregin, Mississauga; Michael K. Georges, Guelph; Gordon K. Hamer; Peter M. Kazmaier, both of Mississauga, all of Canada

73) Assignee: Xerox Corporation, Stamford, Conn. 21 Appl. No.: 358,561 22 Filed: Dec. 14, 1994 51 Int. Cl........................... C08F 2/38; CO8F 10/02 52 U.S.C. .................................... 526/204; 526/270;

526/208; 526/352; 526/193; 526/295; 526/318.6; 526/329; 526/331; 526/339;

526/347; 526/348.5; 526/348.7; 526/348.8 58 Field of Search ................ 526/204, 208, 220, 352 56 References Cited

U.S. PATENT DOCUMENTS

3,682,875 8/1972 Sullivan et al. ..................... 526/220 3,879,360 4/1975 Patron et al. ....................... 526/220 3,954,722 5/1976 Echte et al. ........................... 526/68 4,201,848 5/1980 Kotani et al. ....................... 525/314 4,207,266 6/1980 Opie .................................... 570/144 4,340,708 7/1982 Gruber ................................ 526/313 4,581,429 4/1986 Solomon et al. .................... 526/220 4,736,004 4/1988 Scherer, Jr. et al. ... ... 526/206 4,777,230 10/1988 Kamath ................................. 526/86 5,059,657 10/1991 Druliner et al. ..... ... 525/244 5,100,978 3/1992 Hasenbein et al. ................... 526/86 5,130,369 7/1992 Hughes et al. ....... 5,173,155 2/1992 Caneba ............. ... 526/208 5,216,096 6/1993 Hattori et al. ... ... 526/2O1 5,322,912 6/1994 Georges et al...................... 526/204

FOREIGN PATENT DOCUMENTS

0135280 3/1985 European Pat. Off. . 478838 7/1975 U.S.S.R. .

OTHER PUBLICATIONS

G. Moad et al., “On the Regioselectivity of Free Radi cal Processes; Reactions of Benzoyloxy, Phenyl and

... 524/846

||||||||||||||| USOO5449724A

11. Patent Number: 5,449,724 45 Date of Patent: Sep. 12, 1995

t-Butoxy Radicals with Some a,6-Unsaturated Es ters,” Aust. J. Chem., vol. 36, pp. 1573-1588 (Aug. 1983). A. V. Trubnikov et al., “Inhibition of Polymerization of Vinyl Monomers Using Nitride and Iminoxide Radi cals,” Vysokomol. Soedin, Ser. A, vol. 20, No. 11, pp. 2448-2454 (1978). E. G. Rozantsev et al., “Synthesis and Reactions of Stable Nitroxyl Radicals II. Reactions, Synthesis, pp. 401-414 (Aug. 1971). G. Moad et al., “A Product Study of the Nitroxide Inhibited Thermal Polymerization of Styrene.' Polymer Bulletin, vol. 6, pp. 589-593 (1982). R. Grant et al., "Solvents Effects on the Reaction of t-Butoxy Radicals with Methyl, Methacrylate, Aust. J. Chem. vol. 36, pp. 2447-2454 (1983). S. Bottle et al., “The Mechanism of Initiation in the Free Radical Polymerization of N-Vinylcarbazole and N-Vinylpyrrolidone,' European Polymer J., vol. 25, pp. 671-676 (1989). M. D. Goldfein et al., “Inhibition of Styrene Polymeri zation by the Stable Radical 4,4'-diethoxydiphenylni troxide,' Vysokomol. Soedin., Ser. A, vol. 16, No. 3, pp. 672-676 (1974). M. D. Goldfein et al., “Effect of Free Stable Radicals on the Kinetics and Mechanism of Polymerization of Some Vinyl Monomers,' Vysokomol. Soedin., Ser. A, vol. 17, No. 8, pp. 1671-1671 (1975).

(List continued on next page.)

Primary Examiner-Mark Nagumo Attorney, Agent, or Firm-Oliff & Berridge; Eugene O. Palazzo

57 ABSTRACT

A free radical polymerization process for the prepara tion of a thermoplastic resin includes heating a mixture comprised of a free radical initiator, a stable free radical agent, and ethylene at a temperature of from about 40° C. to about 500 C. and at a pressure of from about 500 to about 5,000 bar to form a thermoplastic resin. The thermoplastic resin has a molecular weight distribution of from about 1.0 to about 2.0,

17 Claims, No Drawings

5.449,724 Page 2

OTHER PUBLICATIONS A. W. Trubnikov et al., "Effect of Stable Radicals on Polymerization of Styrene,' Vysokomol. Soedin., Ser. B, vol. 18, No. 6, pp. 419–422 (1976). A. V. Trubnikov et al., “Mechanism of Inhibition of Vinyl Monomer Polymerization by Stable Radicals, Vysokomol. Soedin, Ser. B, vol. 18, No. 10, pp. 733-736. D. Solomon et al., “A New Method for Investigating the Mechanism of Initiation of Radical Polymeriza tion,” Polymer Bulletin, vol. 1, pp. 529-534 (1979). P. Griffiths et al., “Initiation Pathways in the Polymeri zation of Alkyl Methacrylates with tert-Butoxy Radi cals,” J. Macromol. Sci-Chem., A17(1), pp. 45-50 (1982). G. Moad et al., “Selectivity of the Reaction of Free Radicals with Styrene,' Macromolecules, vol. 15, pp. 909-914 (1982). G. Moad et al., “The Reaction of Acyl Peroxides with 2,2,6,6-tetramethyl-piperidinyl-1-oxy, Tetrahedron Letters, vol. 22, pp. 1165-1168 (1981). G. Moad et al., “The Reaction of Benzoyloxy Radicals with Styrene-Implications Concerning the Structure of Polystyrene, J. Macromol. Sci-Chem., A17(1), pp. 51-59 (1982). P. Griffiths et al., “Synthesis of the Radical Scavenger 1,1,3,3-tetramethylisoindolin-2-yloxyl,' Aust. J. Chem., vol. 36, pp. 397-401 (1983). G. Moad et al., “Reactions of Benzoyloxy Radicals With Some Common Vinyl Monomers. Makronol Chem. Rapid Commun., vol. 3, pp. 533-536 (1982). P. Griffiths et al., “Quantitative Studies of Free Radical Reactions With the Scavenger 1,1,3,3-tetrame

thyl-isoindolinyl-2-oxy, Tetrahedron Letters, vol. 23, pp. 1309-1312 (1982). E. Rizzardo et al., “Initiation Mechanisms in Radical Polymerizations: Reaction of Cumyloxy Radicals with Methyl Methacrylate and Styrene,” Aust. J. Chem., vol. 35, pp. 2013-2024 (1982). M. Cuthbertson et al., “Head Addition of Radicals to Methyl Methacrylate.” Polymer Bulletin, vol. 6, pp. 647-651 (1982). E. G. Rozantsev et al., Synthesis and Reactions of Sta ble Nitroxyl Radicals I. Synthesis, pp. 190-202, 1971. Hans-Georg Elias et al, Macromolecules.2, 2d Ed p. 719, Plenum Press, New York. J. Kochi, “Free Radicals'', vol. I, 16-24, 126-129, 278-281 and 290-293, Wiley, N.Y., 1973. J. K. Kochi, “Free Radicals, vol. II, 88-89, 122-125, 132-135, 166-167 and 382, Wiley, N.Y., 1973. D.C. Non Hekel et al., “Free-Radical Chemistry”, 140-145, 196-203, 208-209, 212-213, 216-217 and 238-241, Cambridge, 1974. W. Funke, "Progress In Organic Coatings', vol. 21, Nos. 2-3, pp. 227-254, Dec. 20, 1992. Owen W. Webster, "Living Polymerization Methods', Science, vol. 251, pp. 887-893, Feb. 22, 1991. Charles H. J. Johnson et al. “The Application of Super computers in Modelling Chemical Reaction Kinetics: Kinetic Simulation of "Quasi-Living Radical Polymeri zation', Aust. J. Chem., vol. 43, pp. 1215-1230, 1990. Ezio Rizzardo, "Living Free Radical Polymerisation, Chemistry in Australia, Jan.-Feb. 1987, p. 32. E. J. Rauckman et al., “Improved Methods For The Oxidation of Secondary Amines To Nitroxides', Syn thetic Communications, vol. 5(6), pp. 409–413 (1975).

5,449,724 1.

STABLE FREE RADICAL POLYMERIZATION PROCESS AND THERMOPLASTIC MATER ALS

PRODUCED THEREFROM

BACKGROUND OF THE INVENTION

This invention relates to improved polyethylene ho mopolymers and random copolymers with controlled narrow molecular weight distributions, and a process for producing such compositions. The process is partic ularly useful in the production of polyethylene homo polymers and random copolymers for use in a wide variety of thermoplastic applications. The present in vention also relates to such polyethylene compositions produced by a stable free radical polymerization pro CeSS.

The polyethylene compositions of the present inven tion may be formed into a variety of thermoplastic products, for example by known processes such as coat ing, rotational molding, thermoforming, extruding, in jection molding and blow molding processes. Examples of such thermoplastic products include kitchenware, coating films over paper or aluminum foil for packag ing, linings for chemical drums and water piping, and uses in electrical wire and cable insulation. In addition, because of its good chemical resistance, polyethylene is found in chemical ware and as a component of electrical apparatus. The production of polyethylene polymers having

varying structure and characteristics is known in the art. For example, low density polyethylene (LDPE) may be made by polymerizing ethylene gas under a pressure of 1,000 to 3,000 bar at temperatures between 120° C. and 350° C. with 0.05 to 0.1% oxygen or perox ide initiators. This reaction may be performed in a tubu lar reactor of about one mile in length by a continuous process. The peroxide initiator, such as benzoyl perox ide, is added as a solution in food grade hydrocarbon solvent at the beginning of the reaction and also in jected into the middle of the reactor. This process pro duces low density polyethylene polymer with a high degree of random branching, where the length of each branch is only about 4 carbon units due to back biting of the chains. The standard conversion of monomer to polymer is typically in the range of 15 to 25 percent with limited control over the molecular weight of the polymer and no control over the polydispersity. As a consequence the upper range of the molecular weight is limited to around 70,000. A high density linear polyethylene polymer with a

molecular weight of about 50,000 can be produced in a solution free radical polymerization process in xylene at from 150° C. to 180° C. at pressures of greater than 35 bar, using Chromium and aluminum silica catalysts. Furthermore, Ziegler-Natta catalysts can be used to synthesize low-pressure high density polyethylene pol ymers. In this process, ethylene is introduced into a dispersion of mixed catalysts such as TiCl4 and alumi num alkyl at a pressure of from 1 to 50 bar and a temper ature of from 20 to 250° C. The ethylene gas polymer izes into almost unbranched, linear high density poly ethylene of medium to high molecular weight with only a small number of short side-chains. The use of stable free radicals as inhibitors of free

radical polymerization is known, for example as de scribed in G. Moad et al., Polymer Bulletin, vol. 6, p. 589 (1982). Studies have also reported on the use of stable free radicals as inhibitors of free radical polymerization

O

15

25

35

40

45

50

55

60

65

2 performed at low temperatures and at low monomer to polymer conversation rates. See, for example, G. Moad et al., Macromol Sci-Chem., A17(1), 51 (1982).

Free radical polymerization processes are also gener ally known in the art. For example, Roland P. T. Chung and David H. Solomon, "Recent Developments in Free-Radical Polymerization-A Mini Review.” Progress in Organic Coatings, vol. 21, pp. 227-254 (1992), presents an overview of the free radical polymerization process, with an emphasis on recent developments.

U.S. Pat. No. 5,322,912 to Georges et. al. discloses a free radical polymerization process for the preparation of thermoplastic resins. The thermoplastic resins are disclosed as having a molecular weight of from 10,000 to 200,000 and a polydispersity of from 1.1 to 2.0. The process comprises heating a mixture of a free radical initiator, a stable free radical agent, and at least one polymerizable monomer compound to form a thermo plastic resin with a high monomer to polymer conver sion ratio, and then cooling said mixture. The polymeri zation process is carried out at a temperature of from 60° to 160° C. and at a relatively low pressure of about 60 psi (about 4 bars). The process optionally comprises isolating the thermoplastic resin or resins and washing and drying the thermoplastic resin. The patent also discloses the preparation of random and block copoly merthermoplastic resins using the free radical polymer ization process. Resins produced by the disclosed pro cess are described as having a narrow molecular weight distribution, and a modality that is controlled by the optional sequential addition of the free radical initiator and stable free radical agent. The patent does not dis close the production of polyethylene homopolymers and random copolymers.

U.S. Pat. No. 5,100,978 to Hasenbein et al. discloses a free radical polymerization process for producing poly ethylene homopolymers and copolymers. The polyeth ylene copolymers include predominant amounts of eth ylene and minor amounts of comonomers that are poly merizable with ethylene. The free radical polymeriza tion process is conducted at a pressure of from 1,500 to 5,000 bar and at a temperature of from 40° C. to 250 C. The process includes at least three separate polymeriza tion stages with fresh initiator being introduced in each stage, wherein polymerization proceeds in the presence of the initiator. The process results in a polyethylene homopolymer or copolymer having a density of more than 925 kg/m3.

U.S. Pat. No. 4,581,429 to Solomon et. al. discloses a free radical polymerization process that controls the growth of polymer chains to produce short chain or oligomeric homopolymers and copolymers, including block and graft copolymers. The process employs an initiator having the formula, in part, equal to =N-O-X where X is a free radical species capable of polymerizing unsaturated monomers. The molecular weights of the polymer products obtained are generally from about 2,500 to 7,000 and have polydispersities generally of from about 1.4 to 1.8. The reactions typi cally have low monomer to polymer conversion rates and use relatively low reaction temperatures, of less than about 100° C., and use multiple stages.

U.S. Pat. No. 4,777,230 to Kamath discloses a free radical polymerization process for producing polymers, wherein monomers are dissolved in solvent with, poly merization initiators (such as peroxide initiators) and an optional chain transfer agent. The polymerization pro

5,449,724 3

cess is conducted at a temperature of from about 90° C. to about 200 C. The resultant polymers have a molecu lar weight distribution of from about 1.5 to about 2.5, and an average molecular weight of less than about 4,000.

Neither of the latter two patents discloses the produc tion of polyethylene homopolymers and random co polymers at high temperature and pressure using a sta ble free radical polymerization process. A problem with conventional polyethylene polymeri

zation processes, however, is that they do not allow for the narrow control of the molecular weight distribution of the polymer or copolymer by a free radical process. The advantage of narrowing the molecular weight dis tribution of polyethylene polymers is reflected in the performance properties of the resultant polymer. A focus in the thermoplastic resin industry has thus been to develop new grades of polyethylene polymers by reducing the molecular weight distribution of the poly Iner.

Among the advantages of a narrower molecular weight distribution is a decrease in the temperature at which the polymer may be later processed. Because longer chain polymers require more energy to soften and mold the polymers, the processing temperature may be decreased as the molecular weight distribution is narrowed. This factor is especially advantageous when working with resins of high shear viscosity. A decrease in the low molecular weight fraction of the polymer observed as a low molecular weight tail in the molecular weight distribution also results in less vola tiles when molding the polymer, thus producing envi ronmentally friendly and safer materials. In addition, eliminating low molecular weight fractions will also contribute to strengthening of the material. Further more, when using polyethylene polymers having a nar rower molecular weight distribution, it is possible to produce thinner films of the polymer, without detri ment to the film's characteristics and properties.

It has been demonstrated that stable free radical poly merization processes can provide precise control over the molecular weight distribution of polymer chains. For example, U.S. Pat. No. 5,322,912, described above, describes a polymerization process that uses stable free radicals to provide thermoplastic resins having a nar row molecular weight distribution. Although it is not desired to be limited by theory, it is believed that when polymerization reaction processes are performed at temperatures above about 100 C., all of the polymer chains are initiated at about the same time. Reversible coupling of the polymer chains by the stable free radical dramatically reduces termination by irreversible cou pling. Therefore, control of the reaction enables the formation of polymer chains having a precise molecular weight and a narrow molecular weight distribution.

SUMMARY OF THE INVENTION

The need continues to exist in the thermoplastic resin industry for improved polyethylene homopolymers and copolymers with improved processing characteristics. Specifically, the need continues to exist for polyethyl ene polymers with narrower molecular weight distribu tions, such that processing of the resultant polymer may be conducted more economically at lower tempera tures. We have discovered that a stable free radical polymerization process may be applied to the produc tion of polyethylene polymers and copolymers to pro vide such polyethylene polymers and copolymers hav

O

15

20

25

30

35

45

50

55

60

65

4 ing a narrower molecular weight distribution, control over the branching and improved processing character istics. Such improved polyethylene polymers and co polymers, and a process for producing such composi tions, are provided herein.

Specifically, this invention provides a free radical polymerization process for the preparation of a thermo plastic resin, comprising heating at a temperature of from about 40 C. to about 500 C. and at a pressure of from about 500 to about 5,000 bar, a mixture comprised of a free radical initiator, a stable free radical agent and ethylene, to form a polyethylene thermoplastic resin, wherein said thermoplastic resin has a molecular weight distribution of from about 1.0 to about 2.0. The polyethylene polymers and copolymers of the

present invention are useful as substitutes for the poly mers and copolymers currently used in the thermoplas tic resin industries. The stable free radical polymeriza tion process disclosed herein is particularly useful in the production of polyethylene resins that have a high shear viscosity. As used herein, high shear viscosity refers to the mechanical properties or the mechanical behavior of the polymer, such as its deformation and flow charac teristics under stress. The mechanical behavior depends on the degree of crystallinity, the degree of crosslinking and the values of the glass transition temperature and the crystalline melting temperature. Polyethylene is a typical flexible plastic with a tensile strength of 2500 N/cm2, a modulus of 20,000 N/cm2 and an ultimate elongation of 500%. The polyethylene compositions of the present invention have narrower molecular weight distributions as compared to traditional polyethylene materials, and possess improved processing characteris tics. Another advantage of using the stable free radical

polymerization process to synthesize homopolymers and copolymers of ethylene is that by protecting the end of the propagating polymer chain with a reversible terminating agent, it is possible to control the rate of addition of the monomer units onto the end of the grow ing chain (the propagation of the polymer chain). Thus, the ability of the radical chain end to react with another polymer chain to produce crosslinking or branching, or to terminate the polymerization, is decreased. Low density polyethylene (LDPE) materials made by cur rent industrial processes have a high amount of branch ing that can not be controlled in the traditional manu facturing process. By using the process of the present invention, the control over the structure of the polymer chain even at low molecular weights is made possible. The present invention thus provides precise control over the length of the main polymer chain. This process can also be extended to medium density polyethylene (MDPE) and high density polyethylene (HDPE) mate rials.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The improved polyethylene homopolymer and co polymer compositions of the present invention may be produced using an improved free radical polymeriza tion process. Generally, the polymerization process involves the free radical polymerization of ethylene gas in the presence of a liquid hydrocarbon medium con taining organic peroxide initiators and/or catalysts. The polymerization process is typically conducted at ele vated temperatures and pressures. However, it has been discovered that by adding a nitroxide stable free radical

5,449,724 5

or other stable free radical agent(s) to the process, and with minor modifications in the temperature and pres sure, a new class of polyethylene homopolymers and random copolymers can be prepared with narrow mo lecular weight distributions. This process may be used to produce polyethylene compositions having a narrow molecular weight distribution, such as from about 1.00 to about 2.5, preferably from about 1.05 to about 2.0, and having a molecular weight in the range of from about 5,000 to about 1,000,000 or greater. The process of the present invention may be applied

to producing low, medium and high molecular weight polyethylene homopolymers and copolymers, and may thus be applied to a variety of industrial applications. For example, the present process may be used to pro duce low molecular weight polyethylenes, such as those having a molecular weight of from about 5,000 to about 60,000; medium molecular weight polyethylenes, such as those having a molecular weight of from about 60,000 to about 200,000; and high molecular weight polyethylenes, such as those having a molecular weight of from about 200,000 to about 1,000,000 or greater. The process of the present invention may be applied

to the free radical polymerization of any monomer that is capable of undergoing a free radical polymerization. However, to provide the improved polyethylene homo polymers and copolymers, ethylene is a preferred mon omer for the polymerization reaction.

Various other monomers may be copolymerized with ethylene to prepare random ethylene copolymers. For example, additional monomers that may be added are those that may undergo free radical copolymerization with ethylene under high pressure, and may include, but are not limited to, propylene; butene; hexene; isobutyl ene; isoprene; butadiene; chloroprene; alpha- or beta ethylenically unsaturated C3-C8 carboxylic acids, such as maleic acid, fumaric acid, itaconic acid, acrylic acid, methacrylic acid and crotonic acid; alpha- or beta-eth ylenically unsaturated C4-C15 carboxylic esters or anhy drides, such as methyl methacrylate, ethyl acrylate, n-butyl acrylate, vinyl acetate, styrene, acrylic acid, methacrylic anhydride, maleic anhydride and itaconic anhydride; mixtures thereof and the like. Generally, any of the various vinyl monomers, and derivatives thereof, may be used as additional monomers to produce the random ethylene copolymers. When copolymers of ethylene and another comono

mer are produced, the comonomer content of the co polymer should not exceed about 50%. The stable free radical agent used in the free radical

polymerization process of the present invention can be any stable free radical agent known in the art. These stable free radical agents are well known in the litera ture; for example G. Moad et al., Tetrahedron Letters, 22, 1165 (1981), which is totally incorporated herein by reference, discloses stable free radical agents as free radical polymerization inhibitors when used attempera tures below 100 C. However, under the free radical polymerization conditions of the present invention, stable free radical agents function as moderators to harness the normally highly reactive and indiscriminate intermediate free radical species. Stable free radical agents are disclosed in U.S. Pat. No. 5,322,912, the entire disclosure of which is incorporated herein by reference. Preferred free radical agents for use in the present invention include those in the nitroxide group of free radicals, for example, PROXYL (2,2,5,5-tetrameth yl-1-pyrrolidinyloxy) and derivatives thereof such as

15

25

30

35

45

50

55

60

65

6 3-carboxyl-PROXYL, 3-carbamoyl-PROXYL, 2,2- dimethyl-4,5-cyclohexyl-PROXYL, 3-oxo-PROXYL, 3-hydroxylimine-PROXYL, 3-aminomethyl-PROXYL, 3-methoxy-PROXYL, 3-t-butyl-PROXYL, 3 maleimido-PROXYL, 3,4-di-t-butyl-PROXYL, 3-car boxylic-2,2,5,5-tetramethyl-1-pyrrolidinyloxy and the like; TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) and derivatives thereof such as 4-benzoxyloxy TEMPO, 4-methoxy-TEMPO, 4-carboxylic-4-amino TEMPO, 4-chloro-TEMPO, 4-hydroxylimine TEMPO, 4-hydroxy-TEMPO, 4-oxo-TEMPO, 4-oxo TEMPO-ethylene ketal, 4-amino-TEMPO, 2.2,6,6-tet raethyl-1-piperidinyloxy, 2,2,6-trimethyl-6-ethyl-1- piperidinyloxy and the like; dialkyl nitroxide radicals and derivatives thereof such as di-t-butyl nitroxide, diphenyl nitroxide, t-butyl-t-amyl nitroxide and the like; DOXYL (4,4-dimethyl-1-oxazolidinyloxy) and deriva tives thereof such as 2-di-t-butyl-DOXYL, 5-decane DOXYL, 2-cyclohexane-DOXYL and the like; 2,5- dimethyl-3,4-dicarboxylic-pyrrole, 2,5-dimethyl-3,4- diethylester-pyrrole, 2,3,4,5-tetraphenyl-pyrrole and the like; 3-cyano-pyrroline, 3-carbamoylpyrroline, 3 carboxylic-pyrroline and the like; 1,1,3,3-tetrame thylisoindolin-2-yloxyl and 1,1,3,3-tetraethylisoindolin 2-yloxyl and the like; porphyrexide nitroxyl radicals such as 5-cyclohexyl porphyrexide nitroxyl and 2,2,4,5,5-pentomethyl-A3-imidazoline-3-oxide1-oxyl and the like; galvinoxyl and the like; and 1,3,3-trimeth yl-2-azabicyclo2.2.2]octane-5-one-2-oxide and 1 azabicyclo3,3,1nonane-2-oxide and the like; mixtures thereof and the like.

Polymerization initiators may be used in the process of the present invention for their known purposes. Initi ators suitable for use in the present process include, but are not limited to, free radical polymerization initiators, such as peroxide initiators and azo initiators. Preferred free radical polymerization initiators for use in the pres ent invention may include, but are not limited to, ben zoyl peroxide, lauroyl peroxide, tert-butyl peracetate, di-tert-amyl peroxide, di-tert-butyl peroxide, tert-butyl hydroperoxide, tert-amyl perpivalate, butyl per-2-ethyl hexanoate, tert-butyl perpivalate, tert-butyl per neodecanoate, tert-butyl perisononanoate, tert-amyl perneodecanoate, tert-butyl perbenzoate, di-2-ethyl hexyl peroxydicarbonate, dicyclohexyl peroxydicar bonate, cumyl perneodecanoate, tert-butyl permaleate, mixtures thereof and the like. Preferred azo initiators may include, but are not limited to, 2,2'-azobis (isobutyronitrile), 2,2'-azobis(2,4-dimethylvaleroni trile), 2,2'-azobis(cyclohexanenitrile), 2,2'-azobis-(2- methylbutyronitrile), 2,2'-azobis(2,4-dimethyl-4- methoxyvaleronitrile), mixtures thereof and the like. Mixtures of two or more initiators can also be used, if desired. The molar ratio of the stable free radical agent to free

radical initiator may be from about 0.4:1 to about 2.5:1, and may preferably be in the range of from about 0.6:1 to about 1.9: 1. Although not wanting to be limited by theory, the molar ratio of stable free radical agent to free radical initiator of about 1.3:1, as preferred in an embodiment of the present invention, is believed to be important for success of the polymerization reaction. If the molar ratio is too high then the reaction rate is noticeably inhibited; but if the molar ratio is too low then the reaction product has an undesired increased molecular weight distribution. The amount of stable free radical agent and free radi

cal initiator used in the polymerization process is di

5,449,724 7

rectly related to the amount of ethylene and other op tional monomers to be polymerized. In embodiments of the present invention, the molar ratio of ethylene and other monomer content to stable free radical agent to free radical initiator may be in the range of from about 100:0.2:1 to about 10,000:2.5:1, and is preferably in the range of from about 300:1.3:1 to about 7,000:1.3:1.

Additionally, the polymerization reaction rate of the ethylene and other monomers may, in embodiments of the present invention, be accelerated and the reaction time reduced by the addition of an organic acid or acids in a molar ratio of stable free radical agent to organic acid(s) in the range of from about 100:1 to about 1:1 and preferably in the range of from about 20:1 to about 5:1. Such acids that may be used in the present invention include, for example, sulfonic, phosphoric or carboxylic acids such as benzoic acid, camphor sulfonic acid, mix tures thereof and the like. The process of the present invention may also incorporate a nitroxide stable radical that contains an acidic functional group, such as 2,2,5,5- tetramethyl-3-carboxyl-1-pyrrollidinyloxy, to increase the rate of reaction without broadening the polydisper sity of the polymeric resins. For example, an effective amount of a protic acid, which will not also initiate cationic polymerization, may be added to the reaction mixture. For example, the protic acid may be selected from the group consisting of organic sulfonic, phos phoric and carboxylic acids and nitroxides containing acid functional groups such as 3-carboxyl-PROXYL, with camphorsulfonic acid being preferred. When such an acid or acid functional group-containing compound is incorporated into the reaction mixture, the molar ratio of stable free radical agent to acid may be from about 100:1 to about 1:1, with a preferred ratio of be tween about 20:1 and about 5:1. Excessive addition of acid beyond the aforementioned amounts may cause the molecular weight distribution of the resultant polymers to broaden.

Additional optional known additives may be used in the polymerization reactions, provided they do not interfere with the objects of the present invention. Such additional additives may provide additional perfor mance enhancements to the resulting product. Such optional additives may include, but are not limited to, colorants, lubricants, release or transfer agents, surfac tants, stabilizers, defoamants, mixtures thereof and the like. The polyethylene polymers are preferably produced

according to the process of the present invention with the virtual exclusion of oxygen. Embodiments of the present invention therefore conduct the stable free radi cal polymerization process in an inert atmosphere, such as under an argon or nitrogen blanket. The polymerization reaction is carried out at high

pressure, such as from about 500 to about 5,000 bar, and preferably at from about 1,000 to about 3,000 bar. The reaction is carried out at a temperature of from about 40° C. to about 500 C., preferably from about 100° C. to about 400° C. and more preferably from about 120° C. to about 350° C. The free radical polymerization process of the pres

ent invention is typically conducted in a liquid hydro carbon medium. As such, it is preferred that the free radical agent, peroxide initiator, and/or any other poly merizable monomers be contained in a hydrocarbon medium prior to heating and initiation of the polymeri zation reaction. The hydrocarbon medium is preferably a non-polymerizable medium, such as, for example,

10

15

20

25

30

35

45

50

55

60

65

8 benzene, toluene, xylene, ethyl acetate, mixtures thereof and the like. Other solvents may be used as necessary to provide a solution of the polymerizable monomers and other components. Where other solvents are used, it is preferred that the solvents are stable under high pres sure free radical polymerization conditions and the polyethylene polymer is soluble in the solvents. The solvent for use in the present invention may thus prefer ably include, for example, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, amyl alcohol, dimeth ylsulfoxide, glycol, dimethylformamide, tetrahydrofu ran, mixtures thereof and the like. The amount of hydrocarbon medium and/or solvent

that permits the preparation of a homogeneous solution of the stable free radical agent, polymerization initiator, and/or monomers may be mentioned as the minimum amount of hydrocarbon medium and/or solvent to be employed in the process. The upper limit of the amount of hydrocarbon medium and/or solvent is determined by practical and economic considerations, since the hydrocarbon medium and solvent have to be separated from the polymer products when the polymerization reaction is completed. Amounts of from about 2 to about 10 parts by weight of hydrocarbon medium and /or solvent per part by weight of the mixture of reac tion components, and preferably from about 4 to about 7 parts of hydrocarbon medium and/or solvent per part of the mixture of reaction components, are often suit able. The stable free radical polymerization process ac

cording to the present invention may be carried out under the temperature and pressure conditions de scribed above. In embodiments, the polymerization reaction may be carried out in either a batch-wise or continuous manner. For example, a continuous reaction may be conducted in an adiabatically operated auto clave or in a corresponding autoclave cascade. Where an autoclave cascade is used, it is possible to use the subsequent autoclave(s) as residence time reactor(s) for completing the conversion of the ethylene and any comonomers. Furthermore, the present polymerization reaction can be carried out in a tubular reactor or in a combination of stirred autoclave and tubular reactor. Operation in series with two stirred autoclaves is partic ularly preferred, since there is the possibility of achiev ing virtually complete conversion of the monomers in the second reactor. The polymerization reaction may also be carried out in a batch reactor, for example, in a continuously stirred tank reactor. Additionally, the polymerization process of the present invention may be carried out using the manufacturing equipment and materials employed in conventional free radical poly merization processes. When the polymerization reaction is completed, or at

a desired suitable percent conversion prior to comple tion, the polymerization reaction may be quenched or terminated by reducing the reaction temperature. For example, the polymerization reaction may be termi nated by reducing the processing temperature to below about 100° C., and preferably below about 40 C.; al though the exact temperature depends upon the specific reactants involved. Following completion or termination of the reaction,

the resultant polymer can be optionally separated from the reaction mixture, washed and dried. Subsequent processing of the polyethylene homopolymer or co polymer can then be conducted.

5,449,724 The above described process can be used to produce

the claimed low, medium and high molecular weight ethylene homopolymers or copolymers, having a de sired molecular weight in the range of from about 5,000 to about 1,000,000 or greater with a narrow molecular weight distribution. The molecular weight of the poly mers may be controlled by adjusting and controlling the various reaction parameters, such as the ratio of mono mer or monomers to initator, reaction temperature, heating temperature profile and conversion of monomer to polymer. For example, as the initiator concentration for a given monomer loading is increased, the molecular weight of the polymer decreases, with other factors held constant. Similarly, as the conversion of monomer to polymer increases, the molecular weight of the resul tant polymer increases. One skilled in the art will recognize that the stable

free radical polymerization process, and the products produced thereby, may be adjusted as necessary to achieve product compositions with specific characteris tics. The invention will now be described in detail with reference to specific preferred embodiments thereof, it being understood that these examples are intended to be illustrative only, and the invention is not intended to be limited to the materials, conditions, process parameters, etc., recited herein. All parts and percentages are by weight unless otherwise indicated.

EXAMPLES Example 1 Into a continuous stirred tank reactor is added ethyl

ene gas. The reactor is pressurized up to 2500 bar and the temperature is increased to 250 C. Once the tem perature and pressure conditions have been established, a solution of benzoyl peroxide initiator and stable free radical agent TEMPO in xylene is added through an injection port in the reactor. The molar ratio of stable free radical agent TEMPO to initiator is 1.3:1. The polymerization of ethylene is allowed to proceed to the desired conversion and molecular weight, while main taining a narrow polydispersity throughout the reac tion.

Example 2 A solution of benzoyl peroxide initiator and stable

free radical agent TEMPO in xylene is added into a continuous stirred tank reactor. The molar ratio of sta ble free radical agent TEMPO to initiator is 1.3:1. The reactor vessel is sealed and is pressurized with ethylene gas to a pressure of 3000 bar while the temperature of 5 the reactor is increased to 250 C. The polymerization of ethylene monomer is allowed to proceed to the de sired conversion and molecular weight, while maintain ing a narrow polydispersity throughout the reaction. What is claimed is: 1. A free radical polymerization process for the prep

aration of a thermoplastic resin, comprising: heating at a temperature of from about 40 C. to about

500 C. and at a pressure of from about 500 to about 5,000 bar, a mixture comprised of a free radical initiator, a stable free radical agent, and ethylene, to form a thermoplastic resin,

wherein said thermoplastic resin has a molecular weight distribution of from about 1.0 to about 2.0.

2. A process according to claim 1, wherein said heat ing is conducted at a temperature of from about 120 C. to about 350 C.

O

15

20

25

35

45

55

60

65

10 3. A process according to claim 1, wherein said heat

ing is conducted at a pressure of from about 1,000 to about 3,000 bar.

4. A process according to claim 1, wherein said stable free radical agent is selected from the group consisting of stable free nitroxide radicals.

5. A process according to claim 4, wherein said stable free radical agent is selected from the group consisting of 2,2,5,5-tetramethyl-1-pyrrolidinyloxy, derivatives of 2,2,5,5-tetramethyl-1-pyrrolidinyloxy, dialkyl nitroxide radicals, derivatives of dialkyl nitroxide radicals, 4.4- dimethyl-1-oxazolidinyloxy, derivatives of 4,4-dimeth yl-1-oxazolidinyloxy, 2,5-dimethyl-3,4-dicarboxylic pyrrole, 2,5-dimethyl-3,4-diethylester-pyrrole, 2,3,4,5- tetraphenyl-pyrrole, 3-cyanopyrroline, 3-carbamoyl pyrroline, 3-carboxylic-pyrroline, 1,1,3,3,-tetrame thylisoindolin-2-yloxy, 1,1,3,3,-tetraethylisoindolin-2- yloxy, porphyrexide nitroxyl radicals, galvinoxyl, 1,3,3- trimethyl-2-azabicyclo2,2,2Octane-5-one-2-oxide, 1 azabicyclo3,3,1nonane-2-oxide, 2,2,6,6-tetramethyl-1- piperidinyloxy, derivatives of 2,2,6,6-tetramethyl-1- piperidinyloxy, and mixtures thereof.

6. A process according to claim 1, wherein said free radical initiator is selected from the group consisting of peroxide initiators and azo initiators.

7. A process according to claim 1, further comprising adding an organic acid to said mixture.

8. A process according to claim 7, wherein said or ganic acid is selected from the group consisting of or ganic sulfonic, phosphoric and carboxylic acids.

9. A process according to claim 1, further comprising adding at least one additional polymerizable monomer to said mixture, wherein said additional polymerizable monomer is copolymerizable with ethylene under free radical polymerization conditions.

10. A process according to claim 9, wherein said additional polymerizable monomer is selected from the group consisting of propylene, butene, hexene, isobutyl ene, isoprene, butadiene, chloroprene, alpha-ethyleni cally unsaturated C3-C8 carboxylic acids, beta-ethyleni cally unsaturated C3-C8 carboxylic acids, alpha ethylenically unsaturated C4-C15 carboxylic esters, al pha-ethylenically unsaturated C4-C15 carboxylic anhy drides, beta-ethylenically unsaturated C4-C15 carboxylic esters, beta-ethylenically unsaturated C4-C15-carboxylic anhydrides, vinyl acetate, styrene, and acrylic acid.

11. A process according to claim 9, wherein said additional polymerizable monomer is added to said

O mixture in an amount of less than about 50 molar per cent of said ethylene.

12. A process according to claim 1, wherein said free radical initiator is selected from the group consisting of tert-butyl peracetate, di- tert-amyl peroxide, di-tert butyl peroxide, tert-butyl hydroperoxide, tertamyl per pivalate, butyl per-2-ethylhexanoate, tert-butyl perpiva late, tertbutyl perneodecanoate, tert-butyl perisononanoate, tert-amyl perneodecanoate, tert-butyl perbenzoate, di-2-ethylhexyl peroxydicarbonate, dicy clohexyl peroxydicarbonate, cumyl perneodecanoate, tertbutyl permaleate, benzoyl peroxide, lauroyl perox ide, 2,2'-azobis(isobutyronitrile), 2,2'-azobis(2,4-dime thylvaleronitrile), 2,2'-azobis(cyclohexanenitrile), 2,2'- azobiso(2-methylbutyronitrile), 2,2'-azobis(2,4-dimeth yl-4-methoxyvaleronitrile), azobisisobutyronitrile and mixtures thereof.

13. A process according to claim 1, wherein said heating is conducted in an inert atmosphere.

5,449,724 11 12

14. A process according to claim 13, wherein said hydrocarbon selected from the group consisting of ben inert atmosphere comprises argon or nitrogen. zene, toluene, xylene, and ethyl acetate.

15. A process according to claim 1, wherein at least 17. A process according to claim 1, further compris one of said free radical initiator and said stable free . A p 8. , Ill p radical agent is dispersed in a hydrocarbon medium. 5 ing cooling said mixture to terminate the polymeriza

16. A process according to claim 15, wherein said tion process. hydrocarbon medium comprises a non-polymerizable :k k k k sk

10

15

20

25

30

35

40

45

50

55

65